Take the first left, then drive for two hours

So I was in the Shell garage, queueing to pay for my petrol because they are a bit backwards and don't have pay@pump, when this Australian couple come in saying they are lost. They go up to the security guard for directions, but he's all "Sorry love, I'm not from round here" or something similar, so they then come to me to ask.

Now, I'm not that good with knowing where to go, even locally, so I wasn't sure I could help them......but it turns out they were trying to get to Stonehenge.....

I don't know exactly where they came from, but I'm thinking to turn up in Watford means they definitely were lost. Anyway, I managed to point them onto the M25 heading for the M3, but I couldn't remember the A road from there, so I hope they are still travelling in the right direction.